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UNIVERSITY OF WATERLOO
Faculty of Engineering
DESIGN AND INSTALLATION OF
INKJET PRINTING SYSTEM ON
A FLATBED ROUTER
Precision Controls Laboratory
University of Waterloo
Waterloo, Ontario
Prepared by
AJung Moon
ID 20163131
3B Mechatronics Engineering
September 15, 2008
September 15, 2008
Dr. Pearl Sullivan, Chair
Department of Mechanical Engineering
University of Waterloo
Waterloo, Ontario
N2L 3G1
Dear Professor Sullivan,
The enclosed report entitled ‘Design and Installation of Inkjet Printing
System on a Flatbed Router’ was written as my fourth work term report (3B) for my
employment at the University of Waterloo.
Under the supervision of Dr. Kaan Erkorkmaz at the Precision Controls
Laboratory my main responsibility was to integrate inkjet printing system on a
flatbed router to build a combined cutting-printing system. The project was carried
out to support the research of a master’s student, Ms. Dayna Chan. This report
documents the completed mechanical and electrical designs for the integration as
well as the selection of necessary components purchased. This report was written
entirely by me and has not received any previous academic credit at this or any
other institution.
I would like to thank Mr. Jeffry Gorniak, Mr. Ammar Alzaydi, and Mr. Sui
Gao for their help in machining mechanical components; Mr. Robert Wagner and
Mr. Andy Barber for their technical assistance during the design and installation
process; and Ms. Dayna Chan and Dr. Kaan Erkorkmaz for providing me with
valuable feedback throughout the project.
Sincerely,
AJung Moon
ID20163131
i
SUMMARY
This report focuses on mechanical and electrical design involved in retrofitting 4’x8’
flatbed router into a combined cutting-printing system. This retrofitting operation
contains three main design sections: selection of vertical axis drive components,
electrical system design, and mechanical design of fixtures.
The first section compares a few common vertical axis drive systems available in
the industries. These configurations include ACME screws, ball-screws, as well as
belt and pulley system. Given the budgetary limit in addition to the requirements
for positioning accuracy a DC servo motor and ball-screw stage is chosen.
The second section briefly describes the electrical design involved in this project.
With emphasis on safe operation of the machine, a 24VDC power supply required to
power the selected vertical axis is connected to the router’s main power. This
configuration ensures that both the router and the inkjet system will immediately
halt when any one of the router’s existing emergency stops are pressed.
The third section describes the mechanical design involved in mounting different
components of the inkjet system. These designs include: mechanical connection
between the new vertical axis and the router, fixture design involved in the
components that travel along the new vertical axis, and modifications on the
router’s gantry for mounting of peripheral components.
All mechanical components have been built, assembled, and installed onto the
router unit. After the retrofit the router’s performance for the three axis of motion
was tested using the machine’s built-in controller.
It is recommended that covers or separators be installed between the router’s
spindle and the printhead mounting unit in order to protect the printhead nozzles
from machined debris. It is also recommended that a sensor be installed near the
printhead nozzles in order to detect the distance between the printing surface and
the printhead nozzles and to avoid collision of the two objects. Upon completion of
electrical work, CSA inspection should be done on both the Z’-axis components as
well as the router. Control algorithms for the Z’-axis printing unit and recharacterization of router’s control parameters should be implemented via PC and
control system platforms such as dSpace.
ii
TABLE OF CONTENTS
Summary .................................................................................................................................. ii
List of Figures.......................................................................................................................... iv
List of Tables ........................................................................................................................... vi
1
2
Introduction ...................................................................................................................... １
1.1
Router ........................................................................................................................ ２
1.2
Xaar 126 Inkjet Printing System .............................................................................. ４
Z’-Axis Stage Selection Process ........................................................................................ ７
2.1
Selection Criteria....................................................................................................... ７
2.2
Drive System Comparison and Z’-Axis Stage Selection ........................................... ８
2.3
Power Component Selection .................................................................................. １１
3
Electrical Design .......................................................................................................... １３
4
Mechanical Design of Inkjet System Mounting ........................................................... １４
4.1
Z’-Axis Stage to Router Interface .......................................................................... １４
4.2
Mounting Inkjet Printing Components on Z’-Axis Carriage ................................ １５
4.2.1
Bottom Plate for Printhead Mounting ........................................................... １６
4.2.2
Supporting Piece for Vertical and Bottom Plate ........................................... １８
4.2.3
Z’-Axis Carriage Overall Assembly ................................................................ １９
4.3
Installation of Ink Supply Peripheral Components.............................................. ２１
4.4
Completed Mechanical Retrofit Overview ............................................................ ２５
5
Conclusion .................................................................................................................... ２６
6
Recommendation .......................................................................................................... ２７
References ............................................................................................................................ ２８
Appendix A: Z’-Axis Maximum Weight Estimation............................................................ ２９
iii
Appendix B: Coupling Calculation ...................................................................................... ３０
Appendix C: Electrical Connection Schematic.................................................................... ３１
Appendix D: Mechanical Drawings ..................................................................................... ３３
LIST OF FIGURES
Figure 1 Two different approaches to the project ................................................................... ２
Figure 2 The 4’x8’ router in isometric view ............................................................................ ３
Figure 3 Z’-Axis drive installation location plan .................................................................... ４
Figure 4 XJ-126 printhead ...................................................................................................... ４
Figure 5 Typical Xaar 126 ink supply schematic [2] .............................................................. ５
Figure 6 LinTech Series 130 linear stage layout ................................................................ １０
Figure 7 Control schematic of Z’-axis.................................................................................. １１
Figure 8 Power supply inside the router control panel ...................................................... １３
Figure 9 Z’-axis moment (M) diagram ................................................................................ １４
Figure 10 Z’-axis stage to router interface assembly .......................................................... １４
Figure 11 Header tank, printhead, and ink trap bottle tube connection [2]...................... １５
Figure 12 XJ-126 printhead mounting angle..................................................................... １６
Figure 13 Single unit bottom plate (a. without printheads; b. with printheads) .............. １７
Figure 14 Multi-unit bottom plate (a. without printheads; b. with printheads) ............... １７
Figure 15 Three different designs of supporting piece ....................................................... １８
Figure 16 Final design of Z’-axis carrier assembly ............................................................. １９
Figure 17 Carriage assembly mechanical component manufacturing sequence ............... ２０
Figure 18 Carriage assembly mounted on Z-axis ............................................................... ２０
Figure 19 Stand-alone filter and pump mounting assembly .............................................. ２１
Figure 20 Filter, pump and ink mounting location proposal 1 .......................................... ２２
Figure 21 Filter, pump and ink mounting location proposal 2 .......................................... ２２
Figure 22 Filter, pump and ink mounting location proposal 3 .......................................... ２３
iv
Figure 23 Isometric view of peripheral component mounting on gantry ........................... ２４
Figure 24 Peripheral component mounting (a. inside gantry cover; b. front of router)..... ２４
Figure 25 Completed retrofit (a. front; b. back) .................................................................. ２５
Figure 26 Z’-axis maximum weight estimation diagram.................................................... ２９
Figure 27 Electrical connection schematic 1....................................................................... ３１
Figure 28 Electrical connection schematic 2....................................................................... ３２
v
LIST OF TABLES
Table 1 Xaar 126 printing system components function and installation notes ................... ６
Table 2 Comparison of different drive mechanisms [3] .......................................................... ８
Table 3 Z’-Axis product comparison chart .......................................................................... １１
vi
1 INTRODUCTION
It has been many years since computer numerical controlled (CNC) machines
became widely used in industries. CNC machines have not only freed human
machinists from laborious and repetitive work on mills, lathes, and routers, but also
allowed rapid and precise manufacturing of products. Recent developments in the
CNC technology and computer-aided manufacturing (CAM) software tools are
constantly improving the complexity, accuracy and repeatability of the finished
products.
The main advantage of a CNC machine is its ability to accurately position its endeffector. This high precision positioning is also highly-desired in other
manufacturing processes. One such process is printing. If printing capability can be
added onto a CNC machine, the machine would be able to cut and print on the same
object. Such dual function machines can be useful in manufacturing large colourful
objects such as signs or engraved doors with printed images. In addition, a
combination of CNC and UV cure printing technology would produce a machine that
can print and engrave on plastic or metal surfaces.
<Company name omitted> has become interested in the idea of a combined cuttingprinting machine using the company’s flatbed router. This project is being
undertaken by the Precision Controls Laboratory at the University of Waterloo
under the supervision of Dr. Kaan Erkorkmaz. The desired final outcome of the
project is to retrofit <Company name omitted>’s router with UV cure printing
technologies.
However, setting up UV cure printing method is in itself a challenging process due
to the complex curing process involved. Hence, the quality of printing from the
router would depend on two independent variables – the configuration of the print
head system on the router as well as the UV curing process. To eliminate this
complexity the initial stage of the project utilizes a solvent based inkjet printing
method as a proof of concept for integrating general printing technology onto a CNC
router. Solvent based inkjet printing is a relatively straight forward printing
method that can eliminate the variables associated with the complex UV cure
process. Once the retrofit of the router is deemed suitable then UV cure printing can
be installed as the final step of the project. Figure 1 is a visual representation of the
two approaches to the project.
１
The Xaar 126, the chosen printing system to be installed onto the router, is
compatible to both solvent and UV based inks. This dual compatibility will allow
the system to convert from solvent to UV based system without requiring any major
modifications.
This report documents the initial stage of the project focusing on the mechanical
and electrical design of components required to retrofit the router and integrate
solvent based inkjet printing system.
x – Router retrofit
y – UV cure process
Figure 1 Two different approaches to the project
1.1 ROUTER
<Company name omitted>’s router is a 4’x8’ flatbed CNC machine with three axes of
motion (X, Y, and Z). The picture of the router is shown in Figure 2.
Each of the three axes has ball-screw drive mechanisms powered by DC motors. The
Y and Z axes have single ball-screw drives and the X-axis uses two ball-screw drives
to support the ends (XLeft, and XRight) of the gantry. Originally the machine only had
２
Figure 2 The 4’x8’ router in isometric view
built-in rotary encoders on each motor. However, linear encoders were added for
XLeft, XRight, and Y axes for more accurate position measurement. Implementation of
feed-forward compensation in combination with linear encoder retrofit has resulted
in 127.09% improvement in overall 2D tracking error, making the position accuracy
of the router to be ±28.53µm. This level of position accuracy is deemed acceptable
for inkjet printing [1].
The functional work area of the CNC router is 2400mm x 1200mm, and the
machine’s maximum tool positioning speed is 250mm/s. A 3hp spindle is located on
the Z-axis and is capable of cutting wood, plastics and metals.
The router can be controlled either by the built-in controller, or by PC and a control
system platform (dSpace). The built-in controller allows basic control of the router
such as performing homing routine and manual positioning of spindle via a joystick
interface. Controls from the PC using RS232 serial interface and MATLAB software
allows much more elaborate control of the router. This configuration will form the
basis of controlling printing trajectory of the machine.
Implementation of Xaar 126 printing system requires a secondary Z-axis to be
installed onto the router. Since the existing Z-axis drive is used for the spindle an
３
additional vertical axis is required in order to keep the printhead nozzles at their
optimum distance above the printing surface independent of vertical motions of the
spindle. This additional Z-axis will be written as Z’-axis from hereafter, and its
planned location is shown in Figure 3.
Figure 3 Z’-Axis drive installation location plan
1.2 XAAR 126 INKJET PRINTING SYSTEM
The Xaar 126 printing system has four XJ-126 printheads (Figure 4) each equipped
with 126 nozzles. These printheads are capable of printing colour images at a
resolution of 300dpi. Each printhead is designated to a single colour of ink – cyan,
magenta, yellow, or black.
Figure 4 XJ-126 printhead
４
Each of the four ink reservoirs are fed into corresponding filters and connected to
the respective ink pumps. Each pump is responsible for sending ink to the header
tanks for maintaining a constant volume of ink in the vessels. Headers tanks supply
ink to the printheads at a constant pressure. The Ink Supply Controller (ISC)
controls the header tanks and ink pumps. ISC can be connected to a PC for realtime status monitoring of the header tanks and pumps. A typical ink supply
schematic is visually represented in Figure 5.
In order to process an image, the computer sends image data to the XUSB controller
via USB interface. Once the image data is received, the XUSB controller determines
the required printing sequence and sends appropriate signals to all four of the
printheads. Since the XJ-126 printhead is an older generation of component relative
to the XUSB controller, the commands from XUSB cannot directly be understood by
XJ-126. Hence, Head Personality Card is used to translate the commands from
XUSB to signals understood by the four XJ-126 printheads. The Xaar 126 printing
system comprises of ten main components. Table 1 provides a summary for their
respective functions and installation notes.
Figure 5 Typical Xaar 126 ink supply schematic [2]
５
Table 1 Xaar 126 printing system components function and installation notes
Component
Function
Quantity
Installation Notes
Printhead that receives
ink from a header tank
and dispenses onto
printing surface via 126
nozzles. Achieves 300dpi
resolution at 36.9 degrees
of tilt angle.
Receives ink from pump
and supplies ink to the
printhead at a correct
pressure.
4
Must be tilted at 36.9
degrees. Nozzle plate must
be parallel to printing
surface with 1mm optimum
gap between printhead
nozzles and printing surface.
4
Pumps ink from filter to
the header tank.
4
Vertical orientation required.
Bottom of header tank must
be 150mm to 350mm above
the printhead nozzles. All
tanks must be at the same
height.
Vertical orientation required.
Ink from the ink reservoir
gets filtered as ink passes
through the filter into the
ink pump. Particles of
size ≥5µm are filtered in
order to prevent nozzle
blockage.
Generates the negative
pressure required by the
header tanks. Controls
switching of ink pumps.
4
Vertical orientation required.
Vent of filter must face
upwards. Minimum distance
to ink pump is desired in
order to minimize required
tube length.
1
Can be mounted in any
orientation. Must be in close
proximity to a PC for
communication.
Receives image from
computer and sends data
to printheads at real time.
Provides power to
printheads.
Supplies 24VDC power to
XUSB controller from
115VAC power source.
1
Must be located near its
power supply. Minimum
distance to a computer is
desirable in order to
minimize length of cables.
Must be located in close
proximity from XUSB due to
cable length limitation
(2.5m).
Head Personality Card(HPC)
Enables the use of XUSB
controller on older
versions of XAAR
printheads such as XJ126.
1
Must be mounted near
printheads. Ribbon cables of
length 30cm need to connect
printheads to the HPC.
Ink Trap Bottle
Prevents inks from being
sucked into the ISC. Acts
as a single air outlet from
ISC to header tanks.
1
Vertical orientation required.
Minimum distance to header
tanks is desired in order to
minimize required tube
length.
Contains inks for
printing.
1 of each
colour (Total
4 bottles)
Vertical orientation required.
Minimum distance to filter is
desired in order to minimize
required tube length.
XJ-126 Printhead
Header Tank
Ink Pump
Filter
Ink Supply Controller (ISC)
XUSB Controller
Power Supply for XUSB
Ink Reservoir
６
1
2 Z’-AXIS STAGE SELECTION PROCESS
As shown in Figure 3, an independent vertical axis needs to be installed beside the
spindle. Since the vertical motion does not require any customization from what is
available in the market different types of drive mechanisms were evaluated. This
section documents the process of choosing the most appropriate Z’-axis drive system.
2.1 SELECTION CRITERIA
The following list of criteria/constraints for selecting Z’-axis drive was compiled
based on the limited information available at the beginning of the project:
Criteria:
1. Minimum vertical travel length of 7”
2. Must be able to carry minimum 3kg of weight vertically
Weight of four printheads is 120grams in total, and weight of printhead mounting plates is estimated
to be 2kg.
3. Positioning speed of 38mm/s or higher
Maximum positioning speed of the router is 250mm/s. 38mm/s is the minimum positioning speed of
the Z’-axis that will not create bottleneck in the printing process.
4. High repeatability
Quality of print will depend on the amount of gap between printhead nozzles and printing surface.
The optimum gap of 1mm should consistently be achieved.
5. Built-in or installable encoder with resolution of less than 10µm
Optimum 1mm gap between surface of print and nozzles is required by the printheads for optimum
quality of print. With maximum 10µm of encoder resolution the maximum deviation from the
optimum gap is ±10%. Tolerance information on the optimum gap is not provided by XAAR, and
such deviation is assumed acceptable.
6. Must not back-drive upon power-off
7. Must have minimum or constant backlash
Constraints:
1. Budget of under $3000 CAD
2. Delivery time of less than 6 weeks
3. Width of 6 inches or smaller
Since Z’-axis will be installed beside Z-axis of the spindle, width of Z’-axis drive system can become a
limiting factor to the functional area of the router if it is greater than minimum width of carriage
mounting plate (estimated width of 6”).
4. Maximum weight of 56.6kg
Assuming the linear guide bearings used to support other axes is used to support the weight of the Z’axis and its components, 56.6kg is the maximum weight of Z’-axis a bearing can support. Calculation
for this value is shown in Appendix A.
７
2.2 DRIVE SYSTEM COMPARISON AND Z’-AXIS STAGE SELECTION
Three different drive mechanisms were considered based on availability and
budgetary limit: ACME screw, ball-screw, and belt & pulley system. Comparison
between the different drive mechanisms is summarized in Table 2.
Table 2 Comparison of different drive mechanisms [3]
Drive
Mechanism
ACME Screw
Ball-Screw
Pros
Cons
-Low operating noise
-High friction prevents backdriving
- Good repeatability
-Low efficiency, high friction
-Low speed
-Low duty cycle
-Low long term life
-Backlash increases with wear
-Easily back-drivable
-Significantly higher prices for
increase in speed
-High efficiency
-High speed
-High duty cycle
-High long term life
-High accuracy and
repeatability
-Constant backlash
Belt & Pulley -High efficiency
-Easily back-drivable
-High speed
-Backlash increases with
-High duty cycle
stretching, tension, and wear of
-Medium long term life
belt
-Good accuracy and
repeatability
-Provides consistent speed
throughout its travel length
-Great for long travel length
applications
Although ACME screw mechanism provides advantages of natural back-drive
prevention, it was deemed inappropriate due to its low efficiency, speed, and duty
cycle. Ball-screw and belt & pulley mechanism both offer high efficiency, speed,
duty cycle as well as good repeatability. The ability of the belt & pulley to provide
long travel lengths were negated for this particular application. Considering the
cost differences, durability, and backlash of the two mechanisms, ball-screw was
selected as the most appropriate candidate for this project.
A number of ball-screw driven stages were found. Each of these products were
compared according to the list of criteria mentioned in section 2.1, and are
summarized in Table 3. Of the five products compared, two met the budgetary
８
constraints as well as the requirements for travel length and rated load. These
products are LinTech Series 130, and Velmex BiSlide 10”. With only $400 difference
LinTech Series 130 product offers significantly faster positioning (127mm/sec) than
BiSlide 10”(32mm/sec), can be equipped with a better resolution encoder (1.27 µm vs
1.6 µm) as well as larger ball-screw diameter for improvement in rigidity. Both
products meet the criteria and constraints outlined in section 2.1, except BiSlide
has slower positioning speed than what is desired (38mm/s). Hence LinTech Series
130 linear stage was chosen as the Z’-axis drive system. A layout of LinTech Series
130 is shown in Figure 6. The stage is equipped with a precision grade ball-screw of
0.625” diameter and 0.2” lead. Two linear bearings attached to one side of the
carriage rides on a stainless steel rail and offers maximum travel length of 8”.
In order to meet the encoder resolution requirement a rotary encoder of 1000ppr is
added onto the stage. The encoder resolution, after taking into account the encoder
quadrature decoding, can be calculated as follows:
(1)
𝑙 = 0.2"/𝑟𝑒𝑣 = 5.08𝑚𝑚/𝑟𝑒𝑣
r = 1000
pulses
rev
counts
× 4 pulses = 4000
counts
rev
l/r = 0.00127 mm = 1.27μm/count
(2)
(3)
where l is the lead, and r is the encoder resolution in cpr. Resolution of 1.27µm
satisfies the encoder resolution criteria.
９
Figure 6 LinTech Series 130 linear stage layout
１０
Table 3 Z’-Axis product comparison chart
１１
2.3 POWER COMPONENT SELECTION
It is desirable to control Z’-axis with the same configuration of control as the router
since this will allow both cutting and printing sequence of the machine to be
controlled by a single controller. A DC servo motor with NEMA23 mounting,
amplifier, and power supply achieves this configuration as shown in Figure 7.
Figure 7 Control schematic of Z’-axis
A spare amplifier, 12A8 from Advanced Motion Controls, was available for the
laboratory use. The 12A8 takes 20 to 80V unregulated DC power from a power
supply, and has maximum continuous current of ± 6 Amps and peak current of ±12
Amps. The amplifier can receive ±10 VDC of analog input from dSpace and send
corresponding amount of current to power the motor.
With the assumed 3kg of weight of the components on carriage, maximum torque
required to move the carriage at maximum acceleration is calculated as below:
𝑎𝑚𝑎𝑥 = 127𝑚𝑚/𝑠 2
𝑚
𝐹 = 9.81 𝑠 2 + 𝑎𝑚𝑎𝑥 ∙ 3𝑘𝑔 = 29.8 𝑁
TRaise =
Fd m
2
∙
𝑙+πfd m
πfd m −f𝑙
= 0.0827 Nm
(4)
(5)
(6)
where 𝑎𝑚𝑎𝑥 is the maximum rated acceleration of the stage, F is the force due to the
weight of the load, 𝑇𝑅𝑎𝑖𝑠𝑒 is the torque required to raise the carriage, 𝑑𝑚 is the
diameter of the ball screw (15.9mm), 𝑙 is the lead of the ball screw, and f is the
coefficient of friction of 0.3.
In order to ensure that the system will not back-drive upon power off, the calculated
torque is used to check the self-locking condition via equation (7):
π ∙ f ∙ dm − 𝑙 = 0.0069
１１
(7)
According to Singley if the value of (𝜋 ∙ 𝑓 ∙ 𝑑𝑚 − 𝑙) > 0 then the system is self-locking
[4]. The resultant value of the equation is very close to 0 indicating that the system
may back-drive with 3kg of load. Hence, an electrical motor brake was deemed
necessary.
Using the value of TRaise calculated from above a DC brush servo motor, Motor
Control Group ID23005, is chosen to raise the estimated load via the ball-screw
mechanism. The motor’s continuous rated torque is 0.402Nm, and peak torque is
2.825Nm with rated speed of 3400rpm. This achieves a safety factor
(𝑇𝐶𝑜𝑛𝑡𝑖𝑛𝑢𝑜𝑢𝑠 _𝑟𝑎𝑡𝑒𝑑 _𝑠𝑡𝑎𝑙𝑙 /𝑇𝑅𝑎𝑖𝑠𝑒 ) of 5 assuming the estimated weight of the load is correct.
The motor consumes 4.14 Amps and 25.90 Amps at stall torque and peak torque
respectively.
Given,
𝑅𝑚 = 2.23 Ω;
𝐾𝑡 = 0.121
𝑁𝑚
𝑇𝑟𝑚𝑠 = 0.58𝑁𝑚;
𝐴
;
𝑉
𝐾𝑒 = 12.7 𝑘𝑅𝑃𝑀 ;
𝜔 = 1500𝑟𝑝𝑚
where 𝑅𝑚 is the motor impedance, 𝐾𝑡 is the torque constant, 𝐾𝑒 is the voltage
constant, and 𝑇𝑟𝑚𝑠 is the root mean square torque, the requirement for the power
supply was derived from the calculation below:
𝑇𝑟𝑚𝑠
= 4.74 𝐴𝑚𝑝
(8)
𝑉𝑒𝑚𝑓 = 𝐾𝑒 ∙ 𝜔 = 19.1𝑉
(9)
𝑉𝑡 = 𝐼𝑚 ∙ 𝑅𝑚 + 𝑉𝑒𝑚𝑓 = 29.7 𝑉
(10)
𝑃 = 𝑉𝑡 ∙ 𝐼𝑚 = 140.6 𝑊
(11)
𝐼𝑚 =
𝐾𝑡
Here, 𝐼𝑚 represents motor current, 𝑉𝑡 indicates motor terminal voltage, 𝑉𝑒𝑚𝑓
represents back emf voltage, and 𝑃 indicates the power required by the motor. The
power required by an optional electrical motor brake is 4.4W and uses 24VDC. One
24VDC power supply for both the motor and brake has been sized. Since the total
required power from the power supply is 145.0W, a 24VDC power supply capable of
minimum 6.0Amps of current was sought. The 240W (24VDC, 10Amp) DLP240-24-1
power supply was chosen, resulting in a factor of safety of 1.7.
１２
3 ELECTRICAL DESIGN
There are two options to providing AC power source to the 240W AC-DC power
supply selected in section 2.3. One is to use the power outlet (115VAC) available on
the walls of the laboratory, and the other is to use the main power (240VAC)
available from the router. Although both options would provide enough AC power to
the power supply, the latter option was deemed more desirable due to safety
reasons.
If the power supply uses a power source other than that of the router’s main power,
then the entire Z’-axis control system shown in Figure 7 would run on a completely
separate circuit from that of the router. This means that a separate emergency stop
circuit will have to exist for the Z’-axis if the machine must halt immediately for
safety reasons. If two different emergency stops are to be pressed at an urgent
situation the purpose of having emergency stop is defeated. Hence, it has been
decided that the power supply will take 240VAC power available from the router’s
main control panel such that the existing emergency stops on the router will halt
both the router as well as the Z’-axis system when pressed.
According to the safety regulations of the CSA electrical code, the power supply
needs to be mounted inside an electrical housing. Instead of building an electrical
housing, the DLP 240-24-1 power supply (4.7”x4.3”x3.8”) is mounted inside a
7”x7”x6” space available in the control panel at the front of the router. Mounted
power supply inside the control panel is shown in Figure 8. Complete electrical
connection schematic is shown in Appendix C.
Figure 8 Power supply inside the router control panel
１３
4 MECHANICAL DESIGN OF INKJET SYSTEM
MOUNTING
Three main sections of mechanical design were involved in mounting all the
required components of the inkjet system from Table 1. First, a mechanical
interface for the Z’-axis was designed in order to link the Z’-axis to the router’s
gantry and Y-axis drive. Second, mountings for printheads and other components to
be carried by the Z’-axis were designed. Lastly, other components that are not
mounted on the Z’-axis carriage – such as filters, pumps, and inks – but need to be
in a close proximity to the axis are mounted on the router gantry.
4.1 Z’-AXIS STAGE TO ROUTER INTERFACE
The simplest way to share the XY axes of the router between the two vertical axes is
to connect the two axis drives with couplings. A set of couplings were designed and
their dimensional parameters were calculated for safety factors. The linkages were
designed to minimize the weight impact on the unit while providing the necessary
structural rigidity. The parallel layout of the links ensures the orientation of the Z’axis unit. Detailed calculation can be found in Appendix B.
These couplings were calculated with the assumption that a set of bearings will be
implemented to take the thrust load of the Z’-axis. Otherwise, there will be moment
created by the weight of the Z’-axis assembly as shown in Figure 9. The moment due
Figure 9 Z’-axis moment (M) diagram
Figure 10 Z’-axis stage to router interface assembly
１４
to the load (W2 in Figure 9) may result in undesirable added dynamics to the router.
Hence, a set of linear bearings (ABBA BRS-40) were implemented to eliminate the
moment and support the weight of the Z’-axis assembly.
The length of the couplings was modified after the mountings on Z’-axis carrier had
been designed such that there would be no interferences between the spindle and
the inkjet printing system mounting assembly. The finalized mounting assembly
for integrating the Z’-axis to Z-axis is shown in Figure 10.
4.2 MOUNTING INKJET PRINTING COMPONENTS ON Z’-AXIS
CARRIAGE
A number of inkjet printing system components listed in Table 1 need to be
mounted onto the Z’-axis carrier. Those components include: four printheads, four
header tanks, a Head Personality Card (HPC), and an ink trap bottle. Printheads,
header tanks, and ink trap bottle must be connected to each other via 3mm tubing.
Figure 11 is an illustration of the assembly for the inkjet printing components.
Electrically, HPC and the printheads need to be connected via four 30cm ribbon
cables. The HPC and header tanks must be connected to XUSB and ISC controller
respectively, both of which are too heavy and large to be mounted on the Z’-axis
carriage. These two electrical connections are mounted externally and the cables
will be fed through the cable tracks from the carriage to their respective controllers.
Electrical schematics between components can be found in Appendix C.
Figure 11 Header tank, printhead, and ink trap bottle tube connection [2]
１５
4.2.1
BOTTOM PLATE FOR PRINTHEAD MOUNTING
Due to the fact that the XJ-126 printheads only have 126 nozzles, the printheads
must be tilted at an angle of 36.9º in order to produce 300dpi resolution image. This
configuration is shown in Figure 12.
Figure 12 XJ-126 printhead mounting angle
In designing a horizontal mounting plate for printheads there were two options: a
single unit mounting plate and individual printhead mouting plates. The individual
mounting plates could be assembled on a larger mounting plate such that their tilt
angle as well as the distance between each other can be fine-tuned. The other option
involved fabricating one large mounting plate that would replace the single
mounting plates.
Considering the latter option, a bottom mounting plate mimicking the dimensions of
adjustment holes of single printhead mounting plates was designed. This design is
shown in Figure 13. However, manufacturing such a mounting plate poses many
problems. First, the angle of the rectangular printhead slots need to be
manufactured at precisely 36.9 degrees. Second, the adjustment holes need to be
threaded for the customized adjustment screw which requires special threading
tools. Not only that, it is difficult to make adjustments to the printhead’s orientation
once the plate has been manufactured and allow for very tight tolerances in
manufacturing the plate. Hence, the option of installing four individual mounting
１６
plates was chosen since it provides greater flexibility and ability to make final
adjustments.
a)
b)
Figure 13 Single unit bottom plate (a. without printheads; b. with printheads)
To ensure the quality of the four single mounting plates to be installed, each of the
plates were measured and inspected carefully. The dimension tolerances between
the different mounting plates were within ±0.20mm deviation, and this was
considered acceptable.
In order to allow maximum adjustment after the bottom plate has been
manufactured, a plate shown in Figure 14 was designed, and was later
manufactured. In this design the individual mounting plates are bolted from the
bottom of the bottom plate through oval shaped holes. The oval shaped holes allow
1mm of shift and angle adjustment of individual printhead mounting plates. This
design only requires simple X and Y axis machining operation on a milling machine
to manufacture the plate.
a)
b)
Figure 14 Multi-unit bottom plate (a. without printheads; b. with printheads)
１７
4.2.2
SUPPORTING PIECE FOR VERTICAL AND BOTTOM PLATE
The orientation of the printhead nozzles with respect to the printing surface is
critical to the quality of the prints. Therefore, it was crucial to create a mechanical
design that ensures accurate horizontal orientation of the bottom plate designed in
section 4.2.1. Three different designs were made, and they are shown in Figure 15.
The first design (Figure 15 a)) uses a standard size angle. It is the easiest to
manufacture, and can produce an angle of nearly perfect 90 degrees. However, this
design is the least rigid of the three designs.
The second design (Figure 15 b)) is similar to the first design, but has added rigidity
in its structure. This design was aimed at providing rigidity while reducing the
most weight from the supporting piece. Although weight reduction from mounting
components is favourable, the efforts involved in machining and necessary
structural analysis outweighs the benefits for the calculated weight reduction.
The third design (Figure 15 c)) offers the most amount of rigidity, and can ensure
the vertical and bottom plates are linked at a accurate 90 degree angle. It is
relatively easier to manufacture compared to the second design. Hence, the third
design was chosen.
a)
b)
c)
Figure 15 Three different designs of supporting piece
１８
4.2.3
Z’-AXIS CARRIAGE OVERALL ASSEMBLY
In order to maintain maximum factor of safety while meeting all of component
installation requirements, efforts were made to reduce the weight of the mounting
plates. Also, additional mounting holes were put in place such that the same
assembly can be easily taken off of the Z’-axis and installed onto the original spindle
axis. This ensures that the assembly can be used for inkjet testing on the Z-axis
when Z’-axis is not functional. The finalized assembly design is shown in Figure 16,
and a breakdown of the components of the assembly is shown in Figure 17. The
overall assembly mounted onto the Z-axis is shown in Figure 18.
This assembly was expected to weigh maximum 3kg in the beginning of the project.
The actual weight measured was approximately 4kg while all components were dry
of ink. Calculations from section 2.3 can be repeated with the new weight to ensure
the motor can indeed drive the assembly upwards.
𝑚
𝐹 = 9.81 𝑠 2 + 𝑎𝑚𝑎𝑥 ∙ 4𝑘𝑔 = 39.8 𝑁
TRaise =
𝐹𝑑 𝑚
2
∙
Factor of Safety =
𝑙+𝜋𝑓𝑑 𝑚
𝜋𝑓𝑑 𝑚 −𝑓𝑙
= 0.112 Nm
T Continuou 𝑠_𝑟𝑎𝑡𝑒𝑑 _𝑠𝑡𝑎𝑙𝑙
T Raise
= 3.5
(12)
(13)
(14)
The factor of safety of the motor is reduced from 5 to 3.5, however, this reduction is
not expected to affect the performance of the Z’-axis system.
Figure 16 Final design of Z’-axis carrier assembly
１９
Figure 17 Carriage assembly mechanical component manufacturing sequence
Figure 18 Carriage assembly mounted on Z-axis
２０
4.3 INSTALLATION OF INK SUPPLY PERIPHERAL COMPONENTS
The header tanks, installed on the Z’-axis carriage, receive inks from its respective
ink pumps via 3mm tubes. It is desirable to maintain all tubes as short as possible
since longer tube length means added hydraulic resistance of the inks. Four other
peripheral components (ink reservoirs, filters, pumps and header tanks) need to be
connected by tubes. Tubes required to connect filters to pumps is minimized by
installing both components onto a single vertical mounting plate. The mounting
plate is designed to keep the two components at the closest proximity and still
taking into account the space required to access the tubes and fittings. A standalone version of the mounting plate complete with filter and pumps is shown in
Figure 19.
Figure 19 Stand-alone filter and pump mounting assembly
There were three options to minimizing the tube length between pumps and header
tanks:
1) Install inks, filters, and pump on the right side of gantry (Figure 20)
In this configuration tubes from pumps to header tanks can be easily fed
through the existing cable track. The right side of the gantry is where the top
cable track starts, and this ensures that there will be minimum turns in ink
tubes from pump to header tank. A disadvantage of this configuration is that
all ink reservoirs, pumps, and filters need to be installed on the same side of
the gantry. This means there will be some undesirable weight imbalance on
the gantry.
２１
Figure 20 Filter, pump and ink mounting location proposal 1
2) Install inks, filters and pumps on the back of the gantry (Figure 21)
In this setup the tubes from pumps to header tanks can be fed from the
middle of the cable track. This solution eliminates approximately 3 ft of
tubing for each colour compared to option 1). When the components are
installed in the centre of the gantry there is no weight imbalance issue. One
disadvantage of this solution is that a longer electrical pump cable is required
compared to option 1). The pump cables for this configuration need to be at
least 3 ft longer than option 1), since the pumps are located farther away
from the right of the gantry where the cable track starts.
Figure 21 Filter, pump and ink mounting location proposal 2
２２
3) Install inks on the back of gantry, and filters and pumps on the
spindle housing (Figure 22)
The mounting plate can be installed on the backside of the spindle housing.
In this setup the tube length would be the shortest since the filter and pump
assembly would travel both X and Y-axis with the Z’-axis assembly. However,
the tubes from ink reservoirs to the filters need to be at least 5 ft long such
that ink can be supplied to the filter even if ink reservoir does not travel
along the Y-axis with filters and pumps.
Figure 22 Filter, pump and ink mounting location proposal 3
Of the three options above, option 3) offered the shortest tube length between the
pump and header tanks. However, while considering option 3) the width of spindle
housing was found to be smaller than the width of the filter and pump mounting
plate. Hence, for the structural stability and ease of installing the filter and pump
mounting plate option 3) was eliminated.
The solution that offers the next shortest tube length is option 2). Although the
difference in tube length between option 1) and 2) is 3 ft per colour, option 2) was
highly preferred over option 1). This is because option 1) not only causes weight
２３
imbalance problem on the gantry, but also is harder to implement due to the nonflat surface of the mounting location. Hence, option 2) was chosen.
Mounting holes were drilled onto the back cover of the gantry in order to support
the filter and pump assembly in the centre. To minimize the tube length between
ink reservoirs to filters the inks were mounted on each side of the filter. The
completed installation of the peripheral components is shown in Figure 23.
Mounting components seen from inside the gantry cover is shown in Figure 24 a. As
shown in the picture all mounting bolts and nuts have minimum 2mm gap from the
Y-axis ball-screw assembly to avoid interferences (Figure 24 b). This design also
allows for easy access and removal of nuts during disassembly of pumps.
Figure 23 Isometric view of peripheral component mounting on gantry
a)
b)
Figure 24 Peripheral component mounting (a. inside gantry cover; b. front of router)
２４
4.4 COMPLETED MECHANICAL RETROFIT OVERVIEW
Shown in Figure 25 is the completed retrofit seen from front and back of the router.
Upon completion of the mechanical installation, the router was tested for its X and
Y axis motion using the built-in controller’s joy-stick interface. No problems were
found in router’s X and Y axis motion during testing. In-depth testing needs to be
done using the PC and dSpace controller in order to determine the changes in the
axis control parameters.
The overall width of the added Z’-axis components is 198.2mm. This means the
overall functional area of the router is reduced from 2400mm X 1200mm to 2400
mm X 1002mm. This more reduction in working area of the router than was
expected (6” or 152.4mm) in the beginning of the project. However, this was
inevitable due to the required spacing of the header tanks and printheads which
were learned later in the project.
Mechanical drawings of all components installed onto the router can be found in
Appendix D. Due to the time constraint of the project, tubes connecting the inkjet
components, and the motor and amplifier for Z’-axis have not been installed yet.
a)
b)
Figure 25 Completed retrofit (a. front; b. back)
２５
5 CONCLUSION
In this project, a flatbed CNC router was retrofitted with Xaar 126 inkjet printing
system in order to combine cutting and printing capabilities. A LinTech Series 130
linear stage was selected to provide the additional vertical axis of motion required
for the retrofit. A mechanical linkage between the stage and the router was made
using two linear guide bearings and four coupling plates that connect the two
vertical axes.
Due to the possibility of the carriage back-driving with a 3kg weight, a 24VDC
electrical brake was implemented. DC servo motor (MCG ID23005) was chosen to
drive the carriage. With the resultant weight of 4kg on the carriage, the factor of
safety calculated by the maximum torque the motor can generate versus maximum
torque required by the linear stage is 3.5.
An amplifier that supplies required current to the motor can be powered by 24VDC
of unregulated power. A 24VDC, 10Amp power supply was chosen for both the
motor and the electrical brake. The power supply’s input power is to come from the
router’s 240VAC main power. This ensures a safe and simple way to share the
existing router emergency stop with the Z’-axis drive system.
Mechanical mounting for components that need to travel along the Z’-axis
throughout the printing operation are mounted onto the carriage of Z’-axis stage. As
a result of the retrofit, the functional width of the router was reduced by 198.2mm.
This reduction in area was inevitable due to the minimum space required by each of
the key components of the assembly, especially the header tanks and printheads.
Lastly, the cover of the gantry was modified to accommodate the filters, pumps, and
ink reservoirs. These components were carefully arranged on the gantry cover in
order to minimize the connecting tube lengths; and hence, ensure minimum
hydraulic resistance in the tubes.
Due to the time constraint of the project, necessary tubing and wiring has not been
finished. However, all mechanical designs were manufactured and installed onto
the router, and did not cause any problems when the router’s three axis of motion
were tested via the machine’s built-in controller.
２６
6 RECOMMENDATION
There are a number of points to be considered before the router becomes fully
functional as a combined cutting-printing machine. They are listed as follows:
1. Cover or separator for printhead nozzles
The printhead nozzles are the most delicate part of the printhead which
needs to be clean of debris at all times. Hence, it would be wise to install a
cover or separator for printhead nozzles such that the debris from cutting
process does not damage the printhead nozzles.
2. Implementation of sensor to meet optimum 1mm distance from
surface
With the installed Z’-axis carriage assembly there is no way of determining
whether the printhead nozzles are 1mm above the printing surface.
Installation of a touch or proximity sensor to determine the distance between
the bottom plate and the printing surface would prevent possible collision
between the carriage assembly and the surface.
3. CSA approval of the overall system once power supply is connected
to the main power of router
It is required that the entire router’s electrical system is inspected by a CSA
agent after it is modified. Once the 24VDC power supply is connected to the
main power of the router the Z’-axis electrical drive components as well as
the router’s electrical system should be inspected and approved by a CSA
agent.
4. Testing of the router’s positioning performance with PC and dSpace
to identify changes in control parameter
Since the mechanical components installed on the router adds some mass to
the gantry, the value of parameters used in the control algorithm may need
to be changed. Hence, the router’s position controller should be modified to
accommodate the changes made to the router.
5. Testing of Z’-axis positioning using PC and dSpace controller
Due to the time constraint of the project, installation and wiring of motor and
amplifier was not finished. This will be completed by an electrician, Andy
Barber. Once this is completed, the Z’-axis must be tested using a PC and
dSpace in order to develop a suitable control algorithm for the axis.
２７
REFERENCES
1. Hang Dong, Improving Gantry Style Router Tracking Accuracy Through
Optical Linear Encoder Retrofit and Error Compensation Using Laser
Interferometry, September 2007
2. Xaar plc, Xaar 126 User Manual: Document D010928009 Version I, 2001,
Accessed July 2008
3. LinTech , Positioning Systems, 2000, Accessed June 2008
4. Singley J. Mechanical Engineering Design. New York: McGraw-Hill. 2003
２８
APPENDIX A: Z’-AXIS MAXIMUM WEIGHT ESTIMATION
Figure 26 Z’-axis maximum weight estimation diagram
Given the assumed weights shown in Figure 26 and MR = 0.12 kN ∙ m (ABBA BRS20 linear guide bearing technical specification),
MR = 9.81 1 ∙ 0.02 + 3 ∙ 0.3 + 𝑥 ∙ 0.2
0.12 × 103 = 9.03 + 1.96𝑥
𝒙 = 𝟓𝟔. 𝟔 𝐤𝐠
where x is the maximum allowable weight of the stage.
２９
APPENDIX B: COUPLING CALCULATION
Assume,
𝑡 = 6.35𝑚𝑚;
𝑤 = 10𝑚𝑚;
𝑑 = 4.9𝑚𝑚;
𝑆𝑦 = 296𝑀𝑃𝑎
where t is thickness, w is width, and d is the diameter of the coupling hole.
Then the stress concentration factor 𝐾𝑡 = 2.2.
σ𝑚𝑎𝑥 = 𝐾𝑡 ∙ 𝑆y = 652𝑀𝑃𝑎
Hence, the coupling will fail upon 652Mpa or higher stress. With 𝐹𝑚𝑎𝑥 = 12.8𝑁 from
free body diagram the expected stress on two couplings connecting the two vertical
axes can be calculated as follows:
σ𝑒𝑥𝑝𝑒𝑐𝑡𝑒𝑑 =
𝐹𝑚𝑎𝑥
= 32.67 kPa
πdt 2 × 2
Therefore, the factor of safety for having two couplings with area of 6.35mm × 10
mm is:
𝜎𝑚𝑎𝑥
𝜎𝑒𝑥𝑝𝑒𝑐𝑡𝑒𝑑
= 19957
Such a large number indicates that even having two coupling to link the two
vertical axes would be fail-safe.
３０
APPENDIX C: ELECTRICAL CONNECTION SCHEMATIC
Figure 27 Electrical connection schematic 1
３１
Appendix C continued
Figure 28 Electrical connection schematic 2
３２
APPENDIX D: MECHANICAL DRAWINGS
1. Z’-Axis Interface Design
３３
３４
３５
2. Z’-Axis Carriage Assembly
３６
３７
３８
３９
４０
４１
４２
４３
４４
４５
４６
４７
４８
3. Filter & Pump Assembly
４９
５０
５１
4. Modified Gantry
５２
５３
５４
５５
５６